1. Field of the Invention
This invention relates to computer hardware and software and, more specifically, to a Video and Audio Front End Assembly and Method.
2. Description of Related Art
Video and audio data signal streams have historically been created, transmitted and displayed in analog format. Most televisions today still accept video and audio signals in analog form and display them without conversion into digital form With the advent of digital televisions and the growing wave of digital broadcast signals, the long-term evolution will be towards creating video in digital format and then maintaining the digital form throughout the transmission and display processes.
That being said, there remains a significant portion of analog video and audio data, both in recorded form and in broadcast form. To use this data in a digital display device, such as a conventional computer, the analog data stream must be converted into digital form. This analog to digital conversion is being done by video decoding assemblies, usually found as subassemblies or “cards” plugged into the “motherboard” of the computer. FIG. 1 depicts the general functionality of a conventional video decoding assembly 10.
The decoding assembly 10 accepts an analog video (and audio) input stream 12, and converts it into a digital video stream in a standard display format 14. Examples of standard display formats include NTSC (adopted in the United States) and PAL (adopted in Europe). While both of these formats are analog, they are not compatible because of their differences in color modulation, field rates, line rates, format and resolution, a signal in PAL format cannot be displayed by a display device designed for NTSC format and vice versa. If we turn to FIG. 2, we can examine the video decoding assembly more closely.
FIG. 2 is a block diagram depicting the subassemblies contained within the conventional video decoding assembly 10. The assembly 10 is typically a circuit substrate 16 having an input receptacle 18 for accepting the analog video/audio input stream 12. The circuit substrate 16 (or “card”) has a plug-in interface built into its bottom edge so that it can be plugged into a “bus” located on the motherboard of the host computer. In order to handle the high-volume data flow of today's digital video, the typical assembly 10 is built to interface with a PCI Parallel bus 32 provided on the motherboard. The conventional PCI Parallel Bus handles a 32-bit or 64-bit data stream (which is the maximum provided on conventional motherboards). New high-performance peripherals require the use of a modem high-speed serial transport such as the PCI Express bus to handle higher data throughput and lower system costs. A PCI Express bus has one or more Lanes of differential transmit and receive pairs, requiring only four signals per Lane while achieving higher data throughput than the parallel 32-bit or 64-bit legacy PCI bus. Examples of devices that use the PCI Express bus include Gigabit Ethernet, Graphics Processors, and IEEE 1394B interfaces.
The assembly 10 has an analog front end (not shown) that receives and conditions the incoming analog video signal 12. Once conditioned, the analog data is passed through an analog-to-digital converter 22. The now-digitized signal then passes through a Channel Matched Filter device 26 and a device for Separating the Audio and Video streams 28 from the input signal stream. The video and audio data streams are then passed to the Video Decoder Device 30V for conversion into the final standardized digital format for display, and to the Audio Decoder Device 30A for conversion into the final standardized audio format for sound. The outputs of the video decoder device 30V and audio decoder device 30A (which are the outputs of the video and audio decoder assembly), denoted here by 14V and 14A, pass through the PCI parallel bus 32 to the host computer 34. A video display software application 36V running within the host computer 34 displays the output 14V of the device 30V on the computer's display and plays the output 14A of the device 30A on the computer's sound system Alternatively, certain devices 30V and 30A will scale the video and process the audio output within the device 44, and not within the host computer.
The problem with the conventional hardware-based video decoding approach is that these devices 30A, 30V (“chips”) are very expensive as compared to the other circuits the make up the host computer and its input interfaces. Furthermore, as mentioned above, the video decoder devices are not cross-compatible with other digital formats. An NTSC device 30V cannot produce video in PAL format. As a result, devices must either designed to support a single standard, or to support multiple standards with additional hardware at greater cost. What is needed is a method for decoding analog video that does not require expensive video and audio decoder devices 30A, 30V and further can provide digital video and audio output in a standardized format that can be chosen (and changed) “on the fly” through software operating on the host computer 34, rather than through hardware replacement.